it may be a vacum regulated system, check for vacum leaks or lose vacum lines. if vehicle has been worked on lately, sometimes things don't get put back on.
Most likely you have a slow antifreeze leak in your heater core which is being sucked onto the windshield.. You may also smell an antifreeze odor.
The warmed water next to the heater becomes hotter when the heater is switched on.
There are heater-resistance wires in the glass of the back windshield.
if you got antifreeze on your windshield when you turn the heater on, it's bad
Misting of a windshield usually indicates a leak in the heater core.
It allows air to circulate through the heater while switched on.
It allows air to circulate through the heater while switched on.
Leaking heater core.Leaking heater core.
Could be the heater core.
That is normal. The ac takes the moisture out of the air and clears the inside of the windshield quickly.
HEATER WISE? YOUR HEATER CORE MAY BE BLOCKED
Sounds like heater core is leaking, replace heater core or bypass